1. Field of the Invention
This invention relates to pyrithione-containing polymers. This invention also relates to the use of these polymers as biocides in paints and wood preservative products.
2. Brief Description of the Prior Art
Biocides are required in many paint and wood preservative formulations to prevent microbial degradation during shipment, storage or use. Biocides are also required in these formulated products to help protect the coated substrate from harmful microorganisms such as bacteria and fungi and the like.
Biocides used in paint products may be grouped into three major classes: preservatives, mildewcides and antifoulants. Preservatives are widely used in water-based paint systems to prevent in-can bacterial and fungal degradation during storage and shipment. They are particularly useful in latex systems such as synthetic rubber, polyacrylate, and natural rubber latexes. Mildewcides are employed to prevent degradation of the dried paint films and underlying substrate by microorganisms. Antifoulant paints are used to prevent the growth of organisms on the hulls of both commercial and pleasure boats. The attachment of such organisms decreases the operating efficiency of the boats and increases their maintenance costs.
Mercurial-type biocides have been widely used as both preservatives and mildewcides in paints. They have excellent performance in both functions in many situations. They offer the fast kill time and can control high levels of bacterial contamination. Unfortunately, they are hazardous to handle and may present environmental problems. Thus, their use may be limited to certain applications. Various nonmercurial preservatives and mildewcides have been increasingly considered as substitutes for mercurial compounds.
A wide variety of biocides have been tried as marine antifoulants, but the marketplace has been dominated by cuprous oxide and organotin compounds for their use. Cuprous oxide has been popular because it is efficient, relatively economical, and is specified in many military antifouling paint formulations as the exclusive biocide. However, this chemical causes microporsity in the paint film, which adversely affects efficiency, and it limits the paint colors to dark reddish brown. The use of organotin compounds has been growing in recent years; however, these compounds are more expensive than cuprous oxide and also more difficult to incorporate into paint formulations. Furthermore, they do not leach out completely during use so that when ships are sandblasted the disposal of the contaminated sand poses difficulties. However, organotins yield uniform, tight films without the microporosity problems associated with cuprous oxide and may be formulated in a wide variety of bright or light colors. For these latter reasons, they are widely used on pleasure boats. Since both cuprous oxide and organotin compounds present technical or environmental problems, there is a need for new and better antifoulant paint biocides.
Biocides are also employed as wood preservative products in order to prevent the rapid deterioration of wood products that are exposed to conditions which promote microbial growth and decay. For example, utility poles, cross ties, piling timbers, freshly milled lumber and fence posts as well as wood chip piles used in pulp manufacture require the incorporation of biocides to stop or control fungal attachment. In the past, two classes of biocides have been employed as wood preservatives. One class is oil-borne preservatives (e.g. creosote and pentachlorophenol) while the second class is water-borne salts (e.g. mixtures of inorganic compounds such as copper, chromium, arsenic and zinc salts). The oil-borne preservatives have been the most widely used biocides for wood preservation. However, products treated with these mixtures may have messy oily surfaces. Also both creosote and pentachlorophenol have been objected to as being environmentally hazardous. The water-borne salts are also toxic chemicals which are dissolved in water and injected into wood products where they become bound to or within the wood. These salts have certain advantages over the oil-borne treatments. They leave a cleaner surface that may be more readily painted. Also, their water soluble characteristics provide savings in solvent costs. However, the use of chromium and arsenic salts also present environmental problems.
Because all of these commercially used wood preservatives present these problems, there is a need for new and better wood preservative biocides.
Separately, zinc and sodium pyrithione (also known as the zinc complex and the sodium salt of `-hydroxy-2-pyridinethione, respectively) are well-known biocides in the cosmetic and hair shampoo fields. However, merely blending these biocides into paint and wood preservative formulations may result in one or more problems. Some of the major problems concern their insolubility in the other constituents of the system and their water solubility. Their paint and wood-preservative constituent insolubility may cause agglomerization of the biocide in the dried film. Their water solubility may cause leaching from the paint film or migration of the biocide in the film. These lead to uneven biocidal protection, environmental problems and reduced service life.
It has been found that these paint or wood preservative constituent insolubility and water solubility problems may be corrected by immobilizing the pyrithione moiety in selected polymers. This attachment of this moiety to these selected polymers results in the formation of a bioactive polymer.
Accordingly, it is an object of this invention to provide a class of bioactive polymers which are effective as preservatives, mildewcides and marine antifoulants in paints as well as wood preservatives.
It is also an object of this invention to provide a class of bioactive polymers which do not have the undesirable characteristics of many present commercial products such as leaching of the bioactive agent, yet, are highly toxic to the organisms of concern but have low toxicity to humans and wildlife as well as be cost competitive.
Still further objects and advantages of the present invention will be apparent from the following description.